The present invention relates to a receiving element for circularly polarized high-frequency signals realized in a planar structure in accordance with the printed circuit technology on a dielectric support, as well as to a planar antenna comprising a network of elements of this type. Obviously, in view of the reciprocity character of an antenna, a receiving element (or an antenna formed by a network of receiving elements) is capable of functioning as a radiating element (radiating antenna) without any modification of its characteristics. This remark holds without any exception throughout the following description, and the word "receiving" can at all times be replaced by the word "transmission".
U.S. Pat. No. 4,054,874, filed on June 11, 1975 and issued on Oct. 18, 1977 to Hughes Aircraft Company, discloses, among other embodiments, a high-frequency antenna formed from elements by means of which circularly polarized signals can be transmitted or received. Each element is assembled from a pair of conducting dipoles which are joined in a cross-wise configuration by means of their central portions to constitute one single device, coupled to the ends of corresponding transmission lines. The lengths of the transmission lines differ by one-quarter of the wavelength associated with the frequency of the transmitted or received signals in order that these useful signals are in phase quadrature.
Such a structure has unfortunately the following disadvantages. On the one hand its electrical asymmetry, predominantly owing to the non-symmetrical excitation (at one single end), causes the existence in the centre of the cross of a critical conductive coupling precisely where the current values are at their maximum, on the other hand the proposed antenna can only receive left-hand circularly polarized signals or right-hand circularly polarized signals (the existance of one of these two possibilities excludes the existence of the other possibility), this polarizing direction being fixed by the direction of polarization of the transmission lines coupled to that dipole which is the longer of the two.